Necessary information about radiators made of aluminum and bimetal
By appointment, a radiator is a unit with the help of which a certain space inside a room is heated. By design, as a rule, it consists of several sections, in each of them the coolant circulates. According to the production method, a special aluminum alloy is poured into molds. These forms are made in the form of sections, which are later connected into a single system. In the 21st century, there should not be any difficulty in manufacturing a heating radiator from aluminum. Why does it seem that such a “household” device as a heating radiator is still classified by experts as a high-tech product?
The best experts in the production of these products and scientific consultants of the heating appliance industry community will tell us about the intricacies of manufacturing aluminum and bimetallic radiators.
The main types and features of modern heating radiators
In total, there are 3 types of aluminum radiators: cast, extruded and combined. Each species has its own production nuances.
Cast radiators consist of one-piece cast sections made under high pressure, with each such section being formed in a mold. Then they are connected into a single radiator using special nipples. To seal the intersection joints, gaskets made of graphite or paronite, high-temperature silicone or other materials are used.
One piece extrusion heatsinks made of extruded aluminum profiles. As the name suggests, such profiles are made by extrusion: an aluminum alloy is pressed through the molds, after which all the individual elements are joined together by welding. Such radiators are non-separable by their design.
Combined aluminum radiators combine the properties of the cast and extrusion radiators listed above. Sections are made of extruded profiles, and elements of horizontal collectors are made by injection molding.
There is also another type that ensures stable operation under conditions of high working pressure — this is bimetallic radiators. The difference from all-aluminum is the presence of a mortgage element — a steel manifold. Sections of this type of radiator for central heating consist of a steel core in the form of thin-walled steel pipes (channel for the passage of the coolant) with external aluminum alloy fins that perform the function of heat transfer. This is done so that the coolant (water) passes through the collector without contact with aluminum.
In the production of radiators, they are primarily guided by the requirements of compliance with GOST 31311–2015 “Heating appliances. General technical conditions».
The most important indicator of safety is static strength, which is ensured by:
— use of high-quality aluminum ingots;
— use of modern melting furnaces and compliance with the melt preparation technology;
— functioning of modern casting machines and fixed casting modes;
— the use of molds of a special design that provides cooling and removal of gases;
— availability of a spectral analysis laboratory for input control of raw materials and melt quality;
— work of qualified personnel (including technologists and operators of casting machines).
In accordance with GOST R 53583–2009 “Heating appliances. Test Methods»  in specialized laboratories that have the necessary equipment to measure heat transfer, strength and tightness, they carry out the necessary tests to confirm the consumer properties of the radiator declared by the manufacturer.
It should be noted that at the moment there is no mandatory certification of heating radiators, therefore all the requirements of GOST 31311–2005 are “good manners” for radiator manufacturers. They are observed by conscientious manufacturers on a voluntary basis.
Are all alloys identical?
GOST 31311–2005 states that cast aluminum radiators must be made from aluminum alloys that provide the required technological and structural parameters of the castings.
The chemical composition of the aluminum alloy significantly affects the thermal and technological properties of the radiator. In accordance with GOST, the alloy of the material is charged (formed) with various additives to achieve the required composition.
The link between production and technology plays an important role. In a specific production, they must adhere to a specific technology developed and existing there. One of the main factors affecting the quality of the final product is the correct design of the system of channels and cavities in the mold, since aluminum alloys are subject to very strong oxidation.
In principle, the basis of aluminum is the same, differing only in the number of components in the alloy. Separately taken production selects a certain alloy for specific tasks. Depending on the manufactured models of radiators, the chemical elements of the material make it possible to achieve the desired physical and mechanical properties of the final product.
Especially for such tasks at good manufacturing plants, it is possible to vary the impurities added to the aluminum alloy. First of all, such is silicon, an increase in the content of which helps to improve the casting properties of the alloy, to give it greater fluidity. Due to this property, manufacturers have the opportunity to cast a radiator with a thinner fin width. As a result, the mass of the radiator is reduced (the surface area does not change, but the amount of material used for manufacturing is less). However, it should be borne in mind that with such a procedure, heat transfer will also decrease.
What standards should be provided for in the preparation of melts? This is degassing, control of the temperature of the melt and its chemical composition.
What defects can occur during the melting of ingots and casting of finished products (affecting the quality of the product and its strength)? It:
— pores, air saturation,
— surface defects,
— low strength and ductility,
— sinks, shrinkage and some others.
What parameters should be monitored? For cast radiators, this is the control of the wall thickness, and in the production of bimetallic radiators, it is the control of the positioning of the embedded element.
First of all, it is necessary to judge the good quality of the radiator by the nominal heat flux (heat output). THeat flow is the power of thermal energy coming from the heating device. Another quality is evidenced by such a characteristic as pworking pressure. Operating pressure — this is the maximum overpressure in the heating system that the radiator design can withstand.
According to GOST 31311–2005, radiators must be strong and tight enough to withstand a test pressure one and a half times the maximum operating pressure. In this case, the destruction pressure for cast radiators must exceed the maximum operating pressure by at least three times. Also, the norms for the permissible deviation of the actual value also exist for heat transfer. They are established according to the results of the tests. The value declared by the manufacturer on the packaging and in the accompanying documentation (in the technical data sheet of the device) must be in the range from ‑4% to +5%.
In addition, it is necessary to take into account a number of factors that affect the value of the heat transfer of the heater. According to many years of research by the MRT laboratory of the Polytechnic University of Milan (Politecnico di Milano), as well as the leading Russian testing laboratories for heating devices of the Research Institute of Plumbing and Vitaterm, a certain dependence of the heat output of the radiator on the material, shape, thickness, surface treatment technology, and on the parameters of the circulation of the coolant inside products.
Quality and its control
Since heating radiators are overwhelmingly located in residential and public buildings, in other words, they are in close proximity to people, in connection with this circumstance, uniform regulatory requirements should be imposed on their safety and quality.
Even at the manufacturing stage, the manufacturers themselves carry out a thorough quality check of heating radiators. Production control is multifactorial and multistage.
The first stage of control — quality control is included in the official duties of the staff: that is, for the worker, and for the foreman, and for the shift supervisor, one of the main motivations is the release of high-quality products.
The second level of control is the technological service, which develops the production technology for each production operation and takes care of compliance with the approved technological maps.
The third degree of control is a special quality service that carries out direct control at each stage of production, as well as complete input control of the material from which the products will be made (spectrographic control): it is simply impossible to smelt a good quality metal without prompt verification of compliance with the chemical composition of the alloy. Such verification according to the norms is carried out in the laboratories of spectral analysis.
In addition, the quality service should be equipped with equipment to check the geometric dimensions of sections, wall thickness, thread quality, as well as to check the tightness and strength of sections and radiators as a whole.
In Europe, in turn, the experience of quality control in the production of radiators is traditionally adopted from Italy, as it is at the head of the list that produces first-class heating appliances. The European manufacturer is obliged to carry out factory production control (FPC) to ensure that the products sold comply with the main parameters of the Declaration of Performance (DoP) (similar to our Russian heater passport). Such a system of production control ensures the achievement of excellent quality and the required technical characteristics of products at the highest level.
From everything we can conclude that in order to produce high quality aluminum or bimetallic radiators, the manufacturer needs to have deep knowledge, skills and abilities in wide areas of mechanical engineering, metallurgy and metalworking, reliable modern equipment and highly qualified personnel.
And in parallel with strict quality control and observing safety requirements, it is possible to produce a reliable and energy-efficient heating radiator. At the same time, it is obvious that only by following state standards can a high result be achieved.
The article was prepared by APRO specialists.
Thank you for your help in preparing this article:
Gianluigi Arici, Deputy Chairman of the Association of Manufacturers of Equipment and Components for Heating Systems Assotermica;
- Renzo MarchesiHead of the Thermal Engineering Research Laboratory MRT (Misure Ricerche Termotecniche) of the Politecnico di Milano;
— Claudio TariniThermal Engineering Research Laboratory MRT (Misure Ricerche Termotecniche) of the Politecnico di Milano;
- Vitaly Sasina, General Director of the testing laboratory “Vitaterm”;
— Vasily Gromov, professor of MAN, scientific secretary of the Research Institute of Sanitary Engineering;
- Herman Bershidsky, Deputy General Director of the Research Institute of Sanitary Engineering for Science;
- Nikolai Salivonchik, Deputy General Director of the largest Belarusian production of aluminum radiators;
- Petra Smirnova, director of strategic development of the Royal Thermo Industrial Group — Campo Di Calore;
— Maxim TorunovDeputy Head of Production of the Industrial Group Royal Thermo — Campo Di Calore.
Interstate standard GOST 31311–2005. Heating devices. General specifications. — M .: “Standartinform”, 2006.
National standard of the Russian Federation GOST R 53583–2009. Heating devices. Test methods. — M. “Standartinform”, 2010.